When it comes to particles and conjunctions especially, it can be difficult to translate every single one. Sometimes the best translation is punctuation, and other times it feels like the word is superfluous and should just be dropped in order to write in proper English.
But extreme caution is urged in the case of the later. There is a reason for every word, even if we don’t understand why it is used.
In Matthew 10 we find the list of the disciples. In v 10 we read, “Simon the Cananaean (Σίμων ὁ Καναναῖος), and Judas Iscariot (καὶ Ἰούδας ὁ Ἰσκαριώτης), who betrayed him (ὁ καὶ παραδοὺς αὐτόν).” ὁ … παραδοὺς αὐτόν is straight forward Greek, a phrase modifying Ἰούδας. But why is καὶ there, and should it be translated?
The CSB translates “who also betrayed him” (also KJV). NLT has, “who later betrayed him.” The NET doesn’t translate the καί, but cryptically adds the footnote, “Grk, ‘who even betrayed him.”
Unfortunately, the NIV, NASB, and NRSV skip the καί. I am not sure why; probably an issue of English style. But then the question becomes, does it have meaning? I think so. Judas is the last of the disciples listed, hence the first καί. But Matthew feels it important to point out that not only is Judas a disciple, but he is also the disciple who betrayed Jesus. I am scratching my head to see why the NASB skips the word.
Do we have to say “also” to make this point? No. Did Matthew feel it was important to say καί to make this point? Yes.
I’d go with Matthew.